1. Field of the Invention
The present invention relates to a magnetic recording apparatus and a magnetic recording medium for use in the recording apparatus.
2. Description of the Prior Art
Conventionally, a magnetic recording medium is used in a type of magnetic printer in which a magnetic latent image is formed on a magnetic recording medium to be developed to a visible image, for example. See, Shunji Imamura, "Chapter 15 Magnetography Printer", Nonimpact Printing, pp. 159-168, CMC, Japan, 1986.
A magnetic printer includes, generally, a recording magnetic drum which is rotatable about its central axis, and has its circumferential surface coated with a magnetic recording medium made from a thin film of CrO.sub.2 or the like on which a latent image is magnetically formable. In the printing process, an erasing device, provided in opposite to the peripheral surface of the recording medium, initially magnetizes the recording medium in a predetermined magnetic orientation. Then, a magnetic recording head forms a magnetic latent image on the recording medium in response to an image signal, and a developer unit processes in turn the latent image into a visible image by supplying toners to the magnetic latent image on the magnetic recording medium. The toners will adhere to portions at which magnetic forces produced by the leaked magnetic field on the surface of the magnetic recording medium intersect the surface of the magnetic recording medium. Thus, the magnetic latent image is developed to a visible image. Following this, the toners forming the visible image on the recording medium is transferred onto a sheet of paper, and fixed on the latter. Finally, remaining toners are cleaned out from the magnetic recording medium, thus completing the printing process.
A magnetic latent image can be formed on a magnetic recording medium not only by the method using a magnetic head, but also by a method using a thermal magnetic head which is adapted to directly heat a magnetic recording medium by a thermal head or a laser beam irradiating the recording medium. The magnetic recording medium can be magnetized in two different orientations: one mainly along the circumferential surface of the recording medium as is referred to as the longitudinal recording method; and the other in the direction substantially perpendicular to the surface of the recording medium as referred to as the vertical recording method. The vertical recording method can in principle achieve highly stable recording with high resolution.
In the vertical recording method, a higher recording efficiency and resolution can be achieved by a proposed method in which a magnetic flux is concentrated by a magnetic recording medium undercoated with a soft magnetic film of high permeability. FIG. 2 plots the vertical components of magnetic force established on the recording medium with respect to the magnetized orientation, which is schematically illustrated in the lower portion of the figure. In this figure, solid arrows 50 and a solid curve 52 indicate the magnetized orientations and the vertical components of the magnetic force in the longitudinal recording method, respectively, whereas phantom arrows 54 and a broken curve 56 indicate corresponding ones in the vertical recording method.
As shown in FIG. 2, in the conventional magnetic recording apparatus and magnetic recording medium, the longitudinal recording method can achieve recording by attracting toners which are a magnetic material by using leaked magnetic flux produced at boundaries B where the direction of magnetization reverses. In contrast, the vertical recording method cannot achieve high density recording, even where domains in which the magnetized orientation is switched are formed, because of small changes in magnetic force at the domains.